Apparatus equipped with an optical keyboard and optical input device

ABSTRACT

An apparatus includes an optical keyboard and an optical input device controlled by a moving object. The input device has at least one diode laser and photo diode for supplying at least one measuring beam to a device window and for receiving radiation reflected by the object placed on the window. The input device may be integrated in the keyboard such that the measuring beam is guided via the positions of the keys to the window.

This application is a 371 PCT/IB03/003571

BACKGROUND INVENTION

The invention relates to an apparatus comprising an optical input devicecontrolled by a moving object and an optical keyboard, which inputdevice comprises at least one optical sensor unit comprising a diodelaser for supplying a measuring beam and converting means for convertingmeasuring beam radiation reflected by the object into an electricsignal, which converting means are constituted by the combination of alaser cavity and measuring means for measuring changes in operation ofthe laser cavity, which are due to interference of reflected measuringbeam radiation re-entering the laser cavity and the optical wave in thiscavity and which are representative of the movement of the object.

DESCRIPTION OF PRIOR ART

An optical keyboard is understood to mean a keyboard having movable keys(buttons) and a flat light guide arranged under the keyboard surface andprovided with means to guide radiation along the positions of the keysand then to a radiation sensitive detector. Each key has a portionwhich, upon pushing the key, moves into a radiation path within thelight guide and causes a change of the amount of radiation received bythe detector via this radiation path.

The moving object is, for example a human finger, but may also be anyobject that is suitable to be moved over a transparent window of theinput device.

The invention is especially intended for use in small hand-heldapparatus, for example a mobile phone, a cordless phone, a hand-heldcomputer, a personal digital assistant or a remote control, for examplefor a TV set. Such an apparatus comprises a flat display panel fordisplaying information either received from external sources or given inby the user or generated by a digital processor (internalmicrocomputer). The apparatus further comprises a keyboard for dialentry, i.e. chose a telephone number, and other functions, likeactivating software programs either stored in the digital processor oravailable from external sources to which the apparatus has access. Forscrolling software menus and selecting a special program of such a menu,the apparatus is provided with an input device controlled by a finger ofthe user.

PCT patent application WO 02/037410 discloses an optical device of thetype mentioned herein above. This input device uses the combination of aDoppler effect and so-called self-mixing effect in a diode laser. Thelatter effect is the phenomenon that radiation emitted by the diodelaser and re-entering the laser cavity induces a variation in the gainof the laser and thus in the radiation emitted by the laser. In thisdevice the window is illuminated by a skew laser beam, which has acomponent in the direction in which the finger is to be moved. If thefinger is moved, the laser radiation scattered by the finger gets afrequency different from the frequency of the radiation illuminating thewindow and the finger, because of the Doppler effect. A portion of thescattered radiation is focussed on the diode laser by the same lens thatfocuses the illumination beam on the finger. Because some of thescattered radiation enters into the laser cavity through the lasermirror, in the laser cavity interference of radiation takes place. Thisgives rise to fundamental changes in the properties of the laser and theemitted radiation. Parameters, which change due to the self-mixingeffect, are the power, the frequency and the line width of the laserradiation and the laser threshold gain. The result of the interferencein the laser cavity is a fluctuation of the values of these parameterswith a frequency that is equal to the difference between the frequencyof the measuring beam and the frequency of the scattered radiation. Thisdifference is equal to the velocity of movement of the finger or anobject in general that is moved relative to the device window. Thus thevelocity of the object and, by integration over time, the displacementof the object can be determined by measuring the value of one of saidparameters. This measuring method can be carried out by means of only afew and simple components and does not require an accurate alignment ofthese components.

An optical keyboard requires one or more LED's (light emitting diodes)or other types of radiation sources and a corresponding number ofradiation sensitive detectors. Each of the radiation sources isaccommodated in an own housing and the space occupied by these housingsand by the detectors may become a problem, especially in hand-heldapparatus. Moreover the radiation sources are relative expensivecomponents and consume much electrical energy. As in hand-held apparatusthe energy is supplied by batteries, such batteries should be rechargedrather frequently, which is annoying for the user.

It is an object of the present invention to provide a new concept ofintegration of the optical input device and an optical keyboard, whichallows considerably reducing the number of components and improving theperformance of the input device. According to the invention theapparatus is characterized in that the path of the measuring beam fromthe diode laser to the window extends through a light guide of theoptical keyboard.

SUMMARY OF INVENTION

The apparatus is based on the insight that measuring beam of the inputdevice can be used also for detecting whether a key of the opticalkeyboard is a pushed condition and on the insight that the reliabilityof the output signal of the input device can be considerably increasedby increasing the distance between the diode laser and the devicewindow. The diode laser of the input is arranged such that the measuringbeam passes all key positions before it reaches the window of the inputdevice.

An embodiment of the apparatus of which the input device allows a/omeasuring of a scroll movement and click movement is characterized inthat the input device comprises two sensor units, which are arrangedrelative to the optical keyboard such that the measuring beam of thefirst and second sensor unit passes on its way to the device window thepositions of a first set of keys and the positions of a second set ofkeys, respectively, the first and second set together comprising allkeys to be controlled.

As explained in WO 02/37410 and input device with two sensor unitsallows measuring of a click movement along a first axis and of a scrollmovement along a second axis, as well as the direction of the scrollmovement (up- or down-scroll). The measuring beams of the first and thesecond sensor units are used to determine the conditions (pushed or not)of the keys of the first and second set, respectively, which sets maycomprise an equal number of keys.

An embodiment of the apparatus of which the input device allows a/omeasuring a click movement and scroll movement in two differentdirections is characterized in that the input device comprises threesensor units, which are arranged relative to the optical keyboard suchthat the measuring beam of the first, the second and the third sensorunit passes on its way to the device window the positions of a first, asecond and a third set of keys, respectively, the first, second andthird set comprising all keys to be controlled.

Again, the measuring beams of the different sensor units are used todetermine the conditions of the keys of the set associated with thesensor unit. An input device per se, which allows measurement alongthree axes, is described WO 02/37410, already mentioned.

A preferred embodiment of the apparatus is characterized in that theinput device comprises a sensor unit adapted to measure both a scrollmovement and a click movement and provided with additional means, whichallow establishing the presence of an object on the window of thedevice.

This input device uses the recently obtained insight that hithertounused information present in a sensor unit, which is used for measuringa scroll movement, can be used to determine the presence of a finger onthe input window. If such a presence is established, it can be concludedthat a click movement, which includes a short rest of the finger on thewindow, takes place. By using a same sensor unit for measuring bothscroll and click movement, a sensor unit can be saved, which means costsand space reduction for the input device, and thus for the apparatus.

The presence of a finger or other object on the input device window canbe determined by measuring amplitude variations of low frequencycomponents in the sensor output signal, or variations in the electricaldrive current for the diode laser of the sensor unit, or the pattern ofundulations in the output signal.

When the preferred embodiment comprises only the adapted sensor unit,its measuring beam passes all positions of the keys of the keyboard.However, the preferred embodiment may comprise a second sensor unit, forexample, for measuring a scroll action along a second axis or forgenerating redundancy in movement information to obtain a more reliablesensor signal and even a third sensor unit for said purposes. In suchcases the measuring beams of the different sensor units control theconditions of different sets of keys.

There are several possibilities to measure changes in operation of thelaser cavity, which results in different embodiments of the apparatus.

A first embodiment is characterized in that the measuring means aremeans for measuring a variation of the impedance of the laser cavity.

A preferred embodiment of the second main embodiment is characterized inthat the measuring means is a radiation detector for measuring radiationemitted by the laser.

The radiation detector may be arranged in such a way that it receivespart of the radiation of the measuring beam.

This embodiment of the input device is, however, preferablycharacterized in that the radiation detector is arranged at the rearside of the laser cavity.

The rear side of the laser cavity is understood to mean the sideopposite the side (front side) where the measuring beam is emitted.

The apparatus comprising a second radiation-sensitive detector formeasuring low-frequency components of modulated measuring radiation maybe further characterized in that the second detector is arranged at theside of the laser cavity where the measuring beam is emitted.

For example, the second detector may be arranged between the diode laserand a lens of the input device either at a position where it receivesradiation reflected by a component of the input device or at a positionwhere it receives radiation split-off from the measuring beam.

The new assembly of optical keyboard and optical input device may beused in different applications, such as in a mobile phone, a cordlessphone, a laptop computer, a hand-held computer, a keyboard for a deskcomputer and a remote control for a TV set.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects of the invention are apparent from and will beelucidated, by way of non-limitative example, with reference to theembodiments described hereinafter. In the drawings:

FIG. 1 a shows, in a cross-section view, an embodiment of a knownoptical input device, which uses the self-mixing effect and by means ofwhich the invention can be implemented;

FIG. 1 b shows a top view of this device;

FIG. 2 shows the measuring principle of this input device;

FIG. 3 shows the variation of the optical frequency and of the gain ofthe laser cavity as a function of the movement of the device and anobject relative to each other;

FIG. 4 shows a method of measuring this variation;

FIG. 5 shows the variation of laser wavelength as a function of thetemperature of the laser with optical feedback;

FIG. 6 shows the effect of the use of a periodically varying drivecurrent for a laser;

FIG. 7 shows how the direction of movement is detected;

FIG. 8 shows a diagram of an optical input device with three measuringaxes;

FIGS. 9 and 10 show an embodiment of a scroll-and-click-input devicehaving two sensor units;

FIGS. 11 and 12 show an embodiment of a scroll-and-click-input devicehaving one sensor unit;

FIG. 13 shows a top view of a mobile phone having an optical keyboard;

FIG. 14 shows a cross-section of this mobile phone;

FIG. 15 shows a top view of an embodiment of the light guides in thismobile phone;

FIG. 16 shows a top view of another embodiment of these light guides;

FIG. 17 shows an embodiment of an integrated optical keyboard andoptical input device having one sensor unit;

FIG. 18 shows an embodiment of an integrated optical keyboard andoptical input device having two sensor units;

FIG. 19 shows an embodiment of an integrated optical keyboard andoptical input device having three sensor units;

FIG. 20 shows a cordless phone apparatus equipped with an integratedoptical keyboard and optical input device;

FIG. 21 shows a laptop computer equipped with an integrated opticalkeyboard and optical input device;

FIG. 22 shows a desktop computer equipped with an integrated opticalkeyboard and optical input device, and

FIG. 23 shows a remote control equipped with an integrated opticalkeyboard an input device.

DETAILED DESCRIPTION

FIG. 1 a shows a diagrammatic cross-section of an embodiment of theknown optical input device. The device comprises at its lower side abase plate 1, which is a carrier for the diode lasers, in thisembodiment lasers of the type VCSEL, and the detectors, for examplephoto diodes. In FIG. 1 a only one diode laser 3 and its associatedphoto diode 4 is visible, but at least a second diode laser 5 andassociated detector 6 may be provided on the base plate, as shown in theFIG. 1 b top view of the device. The diode lasers 3 and 5 emit laser, ormeasuring, beams 13 and 17, respectively At its upper side the device isprovided with a transparent window 12 across which a human finger 15 isto be moved. A lens 10, for example a plane-convex lens is arrangedbetween the diode lasers and the window. This lens focuses the laserbeams 13 and 17 at or near the upper side of the transparent window. Ifan object, like the finger 15, is present at this position, it scattersthe beam 13. A part of the radiation of beam 13 is scattered in thedirection of the illumination beam 13 and this part is converged by thelens 10 on the emitting surface of the diode laser 3 and re-enters thecavity of this laser. As will be explained hereinafter, the radiationreturning in the cavity induces changes in this cavity, which resultsin, inter alia, a change of the intensity of the laser radiation emittedby the diode laser. This is called the self-mixing effect. The intensitychange due to the self-mixing effect can be detected by the photo diode4, which converts the radiation variation into an electric signal. Thissignal is processed in an electronic circuitry 18. The circuitry's 18and 19, shown in FIGS. 1 a and 1 b, for the signal of the photo diodes 4and 6, respectively have only an illustrative purpose and may be more orless conventional. As is illustrated in FIG. 1 b, the circuitry's may beinterconnected.

FIG. 2 illustrates the principle of the input device and the method ofmeasuring when a horizontal emitting diode laser and a monitor photodiode arranged at the rear facet of the laser are used. In this Figure,the diode laser, for example diode laser 3 is schematically representedby its cavity 20 and its front and rear facets, or laser mirrors, 21 and22, respectively. The cavity has a length L. The object or finger, whosemovement is to be measured, is denoted by reference numeral 15. Thespace between this object and the front facet 21 forms an externalcavity, which has a length L₀. The laser beam emitted through the frontfacet, i.e. the measuring beam, is denoted by the reference numeral 25and the radiation reflected by the object in the direction of the frontfacet is denoted by reference numeral 26. Part of the radiationgenerated in the laser cavity passes through the rear facet and iscaptured by the photo diode 4.

If the object 15 moves in the direction of the measuring beam 25, thereflected radiation 56 undergoes a Doppler shift. This means that thefrequency of this radiation changes or that a frequency shift occurs.This frequency shift is dependent on the velocity with which the objectmoves and is of the order of a few kHz to MHz. The frequency-shiftedradiation re-entering the laser cavity interferes with the optical wave,or radiation generated in this cavity, i.e. a self-mixing effect occursin the cavity. Dependent on the amount of phase shift between theoptical wave and the radiation re-entering the cavity, this interferencewill be constructive or negative, i.e. the intensity of the laserradiation is increased or decreased periodically. The frequency of thelaser radiation modulation generated in this way is exactly equal to thedifference between the frequency of the optical wave in the cavity andthat of Doppler-shifted radiation re-entering the cavity. The frequencydifference is of the order of a few kHz to MHz and thus easy to detect.The combination of the self-mixing effect and the Doppler shift causes avariation in the behavior of the laser cavity; especially its gain, orlight amplification, varies.

This is illustrated in FIG. 3. In this Figure, curves 31 and 32represent the variation of the frequency ν of the emitted laserradiation and the variation of the gain g of the diode laser,respectively, as a function of the distance L₀ between the object 15 andthe front mirror 21. Both ν, g and L₀ are in arbitrary units. As thevariation of the distance L₀ is the result of movement of the object,the abscissa of FIG. 3 can be re-scaled in a time axis, so that the gainwill be plotted as a function of time. As explained in WO 02/37410, thegain variation Δg as a function of the velocity v of the object is givenby the following equation:

${\Delta\; g} = {{- \frac{K}{L}} \cdot \cos \cdot \{ {\frac{4{\pi \cdot \upsilon \cdot v \cdot t}}{c} + \frac{4{\pi \cdot L_{0}}}{\lambda}} \}}$In this equation:

K is the coupling coefficient to the external cavity; it is indicativeof the quantity of radiation coupled out of the laser cavity;

ν is the frequency of the laser radiation;

v is the velocity of the object in the direction of the illuminationbeam

t is the moment of time, and

c is the light velocity.

The object surface 15 is moved in its own plane, as is indicated by thearrow 16 in FIG. 2. Because the Doppler shift occurs only for an objectmovement in the direction of the beam, this movement 16 should be suchthat it has a component 16′ in this direction. Thereby, it becomespossible to measure the movement in an XZ plane, i.e. the plane ofdrawing of FIG. 2 which movement can be called the X movement. FIG. 2shows that the object surface has a skew position with respect to therest of the system. In practice, usually the measuring beam is a skewbeam and the movement of the object surface will take place in anXY-plane. The Y-direction is perpendicular to the plane of the drawingin FIG. 2. The movement in this direction can be measured by a secondmeasuring beam, emitted by a second diode laser, and scattered light ofwhich is captured by a second photo diode associated with the seconddiode laser. A (the) skew illumination beam(s) is (are) obtained byarranging the diode laser(s) eccentrically with respect to the lens 10,as shown in FIG. 1 a.

Determining the variation of the laser cavity gain caused by the objectmovement by measuring the intensity of the radiation at the rear laserfacet by a monitor diode is the simplest, and thus the most attractiveway. Conventionally, this diode is used for keeping the intensity of thelaser radiation constant, but now it is also used for measuring themovement of the object.

Another method of measuring the gain variation, and thus the movement ofthe object, makes use of the fact that the intensity of the laserradiation is proportional to the number of electrons in the conductionband in the junction of the laser. This number in turn is inverselyproportional to the resistance of the junction. By measuring thisresistance, the movement of the object can be determined. An embodimentof this measuring method is illustrated in FIG. 4. In this Figure, theactive layer of the diode laser is denoted by the reference numeral 35and the current source for supplying this laser is denoted by referencenumeral 36. The voltage across the diode laser is supplied to anelectronic circuit 40 via a capacitor 38. This voltage, which isnormalized with the current through the laser, is proportional to theresistance, or impedance, of the laser cavity. The inductance 37 inseries with the diode laser forms high impedance for the signal acrossthe diode laser.

Besides the amount of movement, i.e. the distance across which theobject or finger is moved and which can be measured by integrating themeasured velocity with respect to time, also the direction of movementhas to be detected. This means that it has to be determined whether theobject moves forward or backward along an axis of movement. Thedirection of movement can be detected by determining the shape of thesignal resulting from the self-mixing effect. As shown by graph 32 inFIG. 3, this signal is an asymmetric signal. The graph 32 represents thesituation where the object 15 is moving towards the laser. The risingslope 32′ is steeper than the falling slope 32″. As described in WO02/37410, the asymmetry is reversed for a movement of the object awayfrom the laser, i.e. the falling slope is steeper than the rising slope.By determining the type of asymmetry of the self-mixing signal, thedirection of movement of the object can be ascertained. Under certaincircumstances, for example for a smaller reflection coefficient of theobject or a larger distance between the object and the diode laser, itmay become difficult to determine the shape or asymmetry of theself-mixing signal.

Therefor, another method of determining the direction of movement ispreferred. This method uses the fact that the wavelength λ of the laserradiation is dependent on the temperature of, and thus the currentthrough, the diode laser. If, for example, the temperature of the diodelaser increases, the length of the laser cavity increases and thewavelength of the radiation that is amplified increases. Graph 45 ofFIG. 6 shows the temperature (T_(d)) dependency of the wavelength λ ofthe emitted radiation. In this Figure, both the horizontal axis, T_(d),and the vertical axis, λ, are in arbitrary units.

If, as is shown in FIG. 6, a periodic drive current I_(d), representedby the graph 50, is supplied to the diode laser, the temperature T_(d)of the diode laser rises and falls periodically, as shown in graph 52.This results in a standing optical wave in the laser cavity which has aperiodically varying frequency and thus a continuously varying phaseshift with respect to the radiation reflected by the object andre-entering the cavity with a certain time delay. In every half periodof the drive current, there are now successive time segments wherein thediode laser gain is higher and lower, respectively, depending on thephase relation of the wave in the cavity and the reflected radiationre-entering the cavity. This results in a time-dependent intensityvariation (I) of the emitted radiation as shown in graph 54 of FIG. 6.This graph represents the situation for a stationary, or non-moving,object. The number of pulses in a first half period ½p(a) is equal tothe number of pulses in a second half period ½p(b).

A movement of the object causes a Doppler shift of the radiationre-entering the laser cavity, i.e. the frequency of this radiationincreases or decreases dependent on the direction of movement. Amovement of the object in one direction, the upward-, or forward-,direction causes a decrease of the wavelength of the re-enteringradiation, and a movement in the opposite direction, the downward-, orbackward direction causes an increase in the wavelength of thisradiation. The effect the periodic frequency modulation of the opticalwave in the laser cavity has in case the Doppler shift has the same signas the frequency modulation in the laser cavity is different from theeffect in case said frequency modulation and Doppler shift have oppositesigns. If the two frequency shifts have the same sign, the phasedifference between the wave and the re-entering radiation changes at aslow rate, and the frequency of the resulting modulation of the laserradiation is lower. If the two frequency shifts have opposite signs, thephase difference between the wave and the radiation changes at a fasterrate, and the frequency of the resulting modulation of the laserradiation is higher. During a first half period ½p(a) of the drivinglaser current, the wavelength of the generated laser radiationincreases. In the case of a backward moving object, the wavelength ofthe re-entering radiation also increases, so that the difference betweenthe frequencies of the wave in the cavity and that of the radiationre-entering this cavity is lower. Thus the number of time segmentsduring which the wavelength of re-entering radiation is adapted to thewavelength of the generated radiation is smaller than in the case ofabsence of electrical modulation of the emitted laser radiation. Thismeans that, if the object moves in the backward direction, the number ofpulses in the first half period is smaller than if no modulation wouldbe applied. In the second half period ½p(b), wherein the lasertemperature and the wavelength of the generated radiation decrease, thenumber of time segments wherein the wavelength of the re-enteringradiation is adapted to that of the generated radiation increases. Thus,for a backward moving object, the number of pulses in the first halfperiod, i.e. during warming-up of the diode laser, is smaller than thenumber of pulses in the second half period, i.e. during cooling of thediode laser.

This is illustrated in graph 58 of FIG. 7, which graph shows theintensity I_(b) of the laser radiation emitted if the object moves inthe backward direction. Comparing this graph with graph 54 of FIG. 6shows that the number of pulses in the first half period has decreasedand the number of pulses in the second half period has increased. If theobject moves in the forward direction, whereby the wavelength ofradiation scattered by the object and re-entering the laser cavitydecreases due to the Doppler effect, the number of pulses in a firsthalf period ½p(a) is larger than the number of pulses in a second halfperiod ½p(b). This can be verified by comparing graph 56 of FIG. 7,representing the intensity I_(f) of the radiation emitted in the case ofa forward moving object with graph 54 of FIG. 6.

In an electronic processing circuit, the number of photo diode signalpulses counted during the second half period ½p(b) is subtracted fromthe number of pulses counted during the first half periods ½p(a). If theresulting signal is zero, the object is stationary. If the resultingsignal is positive, the object moves in the forward direction and ifthis signal is negative, the object moves in the backward direction. Theresulting number of pulses is proportional to the velocity of themovement in the forward and backward directions, respectively.

Under certain circumstances, for example if the optical path lengthbetween the laser and the object is relatively small and the frequencyand amplitude of the electrical modulation are relatively small, whereasthe movement to be detected is relatively fast, it may occur that thenumber of pulses generated by the Doppler effect is higher than thenumber of pulses generated by the electrical modulation. In suchsituations the direction of movement can still be detected by comparingthe number of pulses during a first half period with the number ofpulses during a second half period. However, the velocity is then notproportional to the difference of these two numbers. In order todetermine the velocity in such situations, the said two numbers shouldbe averaged and a constant value should be subtracted from the result.The number obtained in this way is a measure for the velocity. A personskilled in the art can easily design an electronic circuit for carryingout this calculation.

Instead of the triangular shaped drive current I_(d) used in theembodiment described with reference to FIGS. 6 and 7, also a drivecurrent of another shape, such as rectangular shape, may be used.

The method of measuring the velocity and the direction of the objectmovement described above can also be used if the gain variation isdetermined by measuring the variation of the resistance of the diodelaser cavity.

The measuring method requires only a small Doppler shift, for example interms of wavelength, a shift of the order of 1,5.10⁻¹⁶ m, whichcorresponds to a Doppler frequency shift of the order of 100 kHz for alaser wavelength of 680 mn.

Object movements along two perpendicular (X and Y) directions, ormeasuring axes, in one plane can, be measured with the input device ofFIGS. 1 a and 1 b, which device comprises two diode lasers andassociated photo diodes in a perpendicular orientation. Adding a thirddiode laser and an associated photo diode to the device allows measuringalso the movement along a third, Z-, direction, or measuring axis. Thethird diode laser may be arranged on the optical axis of the lens 10 sothat the third illumination beam is perpendicularly incident on thewindow 12 and the object, or finger, 15 and has no components in theother directions. An optimum measuring signal for the Z direction maythen be obtained. In order to increase the reliability and accuracy ofthe X and Y measuring signals, three diode lasers may be arranged on onecircle and at a mutual angular distance of 120°. This configuration isshown in FIG. 8 wherein the third diode laser and third photo diode aredenoted by the reference numerals 7 and 8, respectively. When the outputsignals of the photo diodes 4, 6 and 8, or the resistance measuringsignals, are represented by S₄, S₆ and S₈ respectively, the objectvelocities V_(x), V_(y) and V_(z) along the X, Y and Z measuring axes,respectively can be calculated, for example, as follows:V _(x)=2.S ₄ −S ₆ −S ₈V _(y)=√3.(S ₈ −S ₆)V _(z)=1/√2.(S ₄ +S ₆ +S ₈)

The electronic circuit for performing this calculation comprises summingand subtracting elements and is relatively easy to implement.

The values of the velocities and, by integration with respect to time,duration of movement, the length of the movement in the X and Ydirections obtained in this way are more reliable and accurate. For,they are the result of averaging the output signals of at least twophoto diodes. Movement errors, or unwanted movements, such as slightlylifting the finger, have a similar effect on the output signals of thephoto-diodes. As the movements along the X and Y measuring axes aredetermined by subtracting output signals from each other, the influenceof an unwanted movement on the X- and Y measuring signal is eliminated.Only the Z-measuring signal, V_(z,), which is obtained by adding theoutput signals of the three photo diodes is indicative of an up/downmovement of the finger or another object.

In applications wherein the movement of a human finger in the Zdirection and the input device relative to each other is used to performa click function, it suffices to detect that such a movement takesplace. An accurate measuring of the displacement of the object is notnecessary so that the Z-measurement may be rather rough. Even thedirection of the movement need not be detected.

Hardly any requirements have to be set to the structure or reflectioncoefficient of the finger. It has been demonstrated that also movementof a piece of blank or even black paper relative to the input device caneasily be measured so that input to the device can also be given byanother object than a finger.

In the input device, such as that shown in FIG. 8, the measuring beamspreferably are not focused in the plane of the window. As these beamoriginate from different positions at the base plate level, themeasuring beams form spots at different positions in the action plane,for example the plane of the window. The measuring beams and theirscattered radiation are sufficient spatially separated, so the crosstalk between the different measuring axes usually does not cause aproblem. If necessary, residual cross talk can be reduced by using diodelasers with slightly different wavelengths. For this purpose, awavelength difference of a few nm is already sufficient.

Another possibility of eliminating cross talk is use of a control drivefor the diode lasers, which causes only one laser to be activated at anymoment. A multiplexing driving circuit, which circuit alternatelyactivates the different diode lasers, may constitute such a controldrive. Such multiplexing circuit allows to monitor two or three diodelasers by means of one detector, or photodiode, which is arranged withinreach of the radiation from each of the diode laser, and is used in atime sharing mode. An additional advantage of the embodiment with such adriving circuit is that the space needed for the circuitry and theelectric power consumption of the device is reduced.

FIG. 9 shows the principle of an embodiment of optical input device,which is typically suited for measuring scroll and click movement. Suchan input device can be used in an apparatus wherein menu charts arescrolled by a cursor on a display and a selected menu activated by aclick. Such an input device, which may be called a scroll-and-clickdevice.

The scroll-and click device 60 of FIG. 9 comprises two optical sensorunits 62, 64. Each sensor comprises a diode laser and photo diodeassembly 66, 68. In the path of each of the measuring beams 74, 76emitted by the diode lasers 66, 68 a lens 70, 72 may be arranged whichfocuses the associated beam in an action plane 78, which may be theplane of the device window. This window 88 may form part of the housing82 of the apparatus in which the device is incorporated, for example amobile phone as shown in FIG. 10. The diode lasers and the associatedlenses are arranged such that the chief rays of the beams 62, 64 are atopposite angles with respect to the normal to the window 88, for exampleat angles of +45° and −45°, respectively.

The object or human finger 80 is moved across the action plane for ascrolling action and moved perpendicular to this plane for a clickingaction. As described herein above, both actions cause a Doppler shift inthe radiation reflected by the finger towards the diode laser and photodiode assemblies 66 and 68. The output signals of the detectorsassociated with these diode lasers are supplied to a signal processingand laser drive electronic circuitry 84. This circuitry evaluates themovements of, for example the controlling finger 80 and suppliesinformation about the said movements at its output 86.

As described herein before a movement of a finger or other objecttowards an away from the laser/diode units may be detected by modulatingthe laser currents and counting the pulses received by the photo diodes.From the output signals Sign₁ and Sign₂ of these diodes, which representvelocities of the object along the chief rays of the beams 74, 76,respectively, the velocity (V_(scroll)) parallel to the window and thevelocity (V_(click)) perpendicular to the window can be calculated asfollows:V _(scroll)= 1/2√2.(Sign₁−Sign₂)V _(click)= 1/2√2.(Sign₁+Sign₂)

FIG. 11 shows an embodiment of a scroll-and-click device 90, used in amobile phone, which device comprises only one optical sensor unit. Thesingle sensor unit comprises a diode laser and photo diode (monitordiode) assembly 92 and a lens 94 to converge the measuring beam from thediode laser on the window 78 of the input device. The monitor diode isconnected to an electronic circuit 98, which processes the monitoroutput signal and controls the laser drive current. Reference number 100denotes the output signal of this circuit or an interface to controlfunctions of the apparatus outside the input device, like mobile phonemenus. As the chief ray of the measuring beam is incident on the windowat a sharp angel, it has a component both in the scroll direction X andthe click direction Z. A scroll movement and a click movement will bothcause a change in the measuring beam radiation reflected back in thelaser cavity. To determine whether it is a scroll movement or a clickmovement that causes such a change, it is established whether the fingeris resting or has rested on the window during a given time duration. Ifthis is the case, it can be concluded that a click action is performed.For, such an action consists of a fast movement in the Z-direction ofthe finger toward the window, a window touch of the finger and a fastretracting of the finger from the window.

As remarked herein above, the frequency of the laser radiationmodulation, which is due to finger movement across the window isdependent on circumstances and, for example, in the order of a few kHzto 1 MHz. It has been found that in case the finger rests on the window,the laser radiation will also be modulated, but at a frequencyconsiderably lower than the scroll frequency. This low-frequencymodulation can be detected by means of an additional detector (photodiode) denoted by 102 in FIG. 11, which is arranged such that itreceives a portion of the modulated radiation. The amount of radiationincident on the photodiode 102 may be set by arranging a beam splitter(not shown), for example a partly reflection mirror, in the path of themeasuring beam. This beam splitter reflects a fixed portion of themeasuring beam radiation towards the additional photodiode. Theadditional photodiode is coupled to the laser drive and signalprocessing circuit 98. This circuit can thus establish whether a clickaction does occur or not, thus whether the measured movement is a clickmovement or a scroll movement.

The occurrence of the low-frequency radiation modulation can also bedetected by means of the monitor diode, as shown in FIG. 12. This Figureshows the assembly 92 comprising the diode laser 104 and the monitordiode 106 for receiving laser radiation 97 emitted at the rear side ofthe diode laser. A portion of the monitor diode signal S_(d) is suppliedto a low-pass filter 108 that passes only the low-frequency componentS_(l) to the signal processing circuit 100. The rest of the signal S_(d)is supplied directly as signal S_(h) to the circuit 98.

Again, in this circuit it is established whether a click movement occursor not, i.e. whether a low-frequency amplitude variation occurs or not,thus whether the measured movement, i.e. the information of S_(h) is aclick movement or a scroll movement. It is also possible to supply thewhole signal S_(d) to the circuit 98 and that this circuit isolates thelow-frequency component from the signal S_(d).

During the time that the finger rests on the window, an opto-electronicfeedback loop exists, which loop encompasses the diode laser and thedevice window, between which elements measuring beam radiation passesforth and back, the monitor diode and the laser drive circuit. Theeffect of coupling back laser radiation in the laser cavity is that thesame amount of radiation is emitted at smaller laser drive electricalcurrent. When a finger is present on the window the drive currentdecreases so that such a presence can be established by measuring thisdrive current, for example in the circuit of FIG. 4 or a similar circuitwell known to a person skilled in the art. The result of such ameasurement allows determining whether the movement measured with themonitor diode is a click movement or a scroll movement.

In case a pulsed diode laser is used, the presence of a finger on thedevice window can also be established by means of counting the number ofundulations in the detector signal occurring in the first and secondhalf of a laser drive current period. As explained at the hand of FIGS.6 and 7, the number of undulations in a first half period will be equalto the number of undulations in the second half period if the fingerrests on the window.

Each of the embodiments of the method to detect the presence of a fingeron the input window described herein above may be combined with one ormore of the other embodiments to obtain redundancy and thus to increasethe reliability of the measurement.

Each of these embodiments may also be used in combination with one ofthe methods of measuring the variations in the laser cavity due to theself-mixing effect and the Doppler shift.

FIG. 13 shows a front view of an embodiment of a mobile phone apparatuscomprising a display panel 112, a microphone 114, an optical inputdevice, represented by the device window 116, and an number pad 118. Thenumber pad is a simplified type of 20 keyboard and comprises a smallernumber of keys, for example dial keys 122 and a few other keys 120. Thenumber of keys may be larger than shown in FIG. 13. Instead of a numberpad, the apparatus may also comprise a keyboard having morecapabilities.

The optical input device can provide great advantages when integrated ina mobile phone, which is provided with a standard protocol, such as theWAP protocol or the I-mode Internet protocol. By means of such aprotocol the mobile phone can be used as a terminal for a worldwidecommunication network, such as the Internet. The window 116 of theoptical input device can be embedded in a side surface 126 of the casing124 of the mobile phone, as shown in FIG. 13. It is also possible toarrange this window in the surface of this casing wherein the number padis accommodated. This window is preferably a convex surface, as shown inFIG. 13. This has the advantage that the window can not collect dirt andgrease and that it can easily be detected by a human finger. The numberpad or keyboard 118 is an optical keyboard.

To demonstrate the impact of the invention on the type of apparatusdiscussed here, first the optical keyboard described in the pending PCTpatent application having filing number PCT/IB02/01859 will be shortlydiscussed.

FIG. 14 shows a cross-section, along the line II-II″ of FIG. 13, of themobile phone. The display 112 may be a liquid crystal display comprisinga layer of liquid crystal material (not shown) arranged between twosubstrates 130, 132. In this embodiment the display is positioned on atransparent carrier (substrate) 134, which is provided with recesses 136at the positions of the keys 122. The substrate 134 is made, forexample, of transparent plastics and comprises a light guide portion andspaces for at least one light source and detector.

In the top view shown in FIG. 15 the light guide portion 140 of thekeyboard (hereinafter keyboard light guide) is situated within therectangular ABCD. At side AD of the keyboard light guide a further lightguide 144 is arranged. This light guide (hereinafter source light guide)receives radiation from a source, for example a LED, which is arrangedat position 142 in the substrate. A similar source light guide 144′ maybe arranged at the side AB of the keyboard light guide to receiveradiation from a second light source, which is arranged at position 142′in the substrate.

The keyboard light guide 140 is constructed, for example is providedwith protruding elements, such that light from the source light guidesis coupled into the keyboard only at positions of light paths 152 in theX direction and light paths 154 in the Y direction. At positions 156where light paths 152 cross light paths 154 a recession is present, asalready shown in FIG. 14. Along side BC of the keyboard light guide 140a further light guide 146 is arranged. This light guide (hereinafterdetector light guide) receives radiation from the keyboard light andtransport this radiation to an optical detector, for example a photodiode, arranged at position 148 in the substrate 134. A similar detectorlight guide 146′ may be arranged at the side CD of the keyboard lightguide 140 to transport radiation from the latter guide to an opticaldetector arranged at position 148′ in the substrate. To improve couplingof radiation from the keyboard light guide into the detector lightguides the latter may be provided with protruding elements.

When a key 122 is pushed, it moves into the keyboard light guide andinto the light paths crossing at the key position 136. Such a key will,partially or totally, reflect light travelling along these paths. As aconsequence, the amount of radiation received by the optical detectorsat positions 148 and 148′ will change so that the output signals ofthese detectors will change. As the source light guides are illuminatedfrom one side by their associated light sources, the intensity of theradiation coupled into the keyboard light guide decreases withincreasing distance of the light paths 152 and 154 from the positions142′ and 142, respectively of the light sources. Thus, the change inamplitude of the detector output signal caused by pushing a particularkey depends on the distance of this key from the light source.

The output signals of the detectors, or photo diodes, are supplied toelectronic circuits for measuring, if necessary after amplification, thechanges in these signals for both the light paths 152 and light paths154 thus allowing to determine which key of the board has been pushed.

The key portions that are pushed into the keyboard light guide may beprovided with a reflective material to improve their capability toreflect the radiation.

The light sources (LED's) may be pulsed sources.

Instead of by means of photodiodes at positions 148 and 148′, theradiation from the keyboard light guide, which is to be measured, canalso be guided to other positions, for example by means of reflectors orother optical components. For example, if the display 112 is controlledby a matrix of thin film transistors, this matrix may be enlarged withadditional transistors for measuring radiation from the keyboard. Thisoption is attractive when substrate 134 is used as display substrateinstead of substrate 130 in FIG. 14. When necessary the design of theadditional transistors can be optimized for their special function.

To couple radiation portions from the source and having differentintensities into the different Y light paths 154, the source light guide144 may show a decreasing thickness, as shown in FIG. 16. A beam portion165 from a source (LED) 160 is reflected as beam 165′ into an Y lightpath 154 by the skew upper side of the source light guide 144 towards akey in that light path. When the key is pushed down its reflectingportion partially reflects the radiation as beam 165 ^(II) towards thedetector light guide 146′. The skew left side of this light guidereflects the radiation as beam 165 ^(III) towards the detector 162. Toimprove the reliability of the measurement, also the radiation passed bythe key reflective portion, as beam 165 ^(IV), can be measured. Thisbeam is reflected by the skew surface of the detector light guide 146′towards the second detector 162′. In the same way the pushed downsituation of the key can be detected via the X light path by means ofthe radiation source 160′, the source light guide 144′, the detectorlight guide 146 and the detector 162′. For this type of detection thelight sources 160 and 160′ should be switched on and off alternately.

It is not necessary to detect the position of the key continuously, itsuffices to do such detection a number of times per second.

The radiation beams sent along the different X and Y light paths 152 and154 can be distinguished not only by different intensities, but also bydifferent frequencies. This can be realized by arranging a colour filter170 between the source light guide 144, 144′ and the keyboard lightguide 140. This filter shows over its lengths a varying colour, forexample, from (infra) red to (ultra) violet. In the detector branch(es)also colour discrimination should be realized. There are severalpossibilities to set the intensities of the radiation beams incident onthe different X and Y light paths, especially by giving the reflectingsurface of the source light guides a specific structure and/or shape.

According to the invention the design of an optical number pad orkeyboard shown in FIGS. 13-16 or a keyboard of another type can besimplified considerably by integrating the keyboard and the opticalinput device. As the beam(s) for determining the conditions of the keysis (are) supplied by the diode laser(s) and measured by means of thedetector(s) of the input device, the keyboard itself no longer needs tocomprise radiation sources and detectors. As the position of a pushedkey is measured in a way different from that discussed at the hand ofFIGS. 13-16, the source light guide 144, 144′ having the specificconstruction and the detector light guide 146, 146′ are no longerneeded. Also the electronic circuits for processing the output signalsof the detectors 148,148′ are no longer needed because information aboutthe position of a pushed key is derived from the output signal(s) of theinput device. In this way considerable space and costs for the opticalkeyboard can be saved. This holds also for other types of opticalkeyboards. Moreover, guiding the measuring beam(s) along the positionsof the keys means that the distance between the diode laser and theobject (finger) to be measured is substantially increased, which resultsin a substantial increase of the accuracy and reliability of the inputdevice. Integration of the optical keyboard and the optical input devicethus provides advantages not only for the keyboard, but also for theinput device.

FIG. 17 shows a first embodiment 180 of an optical keyboard wherein aninput device is integrated. The optical input device comprises a diodelaser and photo diode assembly 182 and a device window 186. The assembly182 is arranged in the keyboard light guide 140 so that the measuringbeam 184 emitted by the diode laser propagates through the light guide140. The assembly 182 may also contain lens means (not shown) tocollimate the measuring beam. Before the device window 186 lens means(not shown) may be arranged in the measuring beam path to converge themeasuring beam on the device window. The measuring beam is guided alongthe positions of all keys by means of mirrors 190-195 before it arrivesat the window.

Scroll movement of the object of finger across the window 186 ismeasured in the same way as described at the hand of FIGS. 1-8. In theembodiment of FIG. 17 the single sensor unit also measures a clickmotion. As described herein before, use is made then of additionalinformation, like a change in the laser drive current, the occurrence ofa low-frequency modulation in the detector signal etc., to detect atemporally presence of the finger on the device window and thus whethera click movement takes place. To measure whether and which key ispressed used is made of the undulations shown in FIG. 6, whichundulations are caused by reflecting measuring radiation returning intothe laser cavity irrespective of a finger movement. Up to now theseundulations, which may be called zero order undulations, have been usedto distinguish between a forward and backward scroll movement. To thatend the zero order undulations are added to or subtracted from theundulations caused by a scroll movement, dependent on the direction ofthe movement. According to the invention a second use is made of zeroorder undulations in the detector output signal. The keys are providedwith optically scattering or retro-reflecting surfaces, which when a keyis pressed, ranges in the keyboard light guide and scatter and reflect,respectively measuring radiation to the laser cavity. As the number ofzero order undulations is dependent on the distance between the diodelaser and the position at which scattering occurs, the position of apressed key and thus the number of this key can be determined bycounting the number of zero order undulations. As in the input devicedescribed herein before already undulations are counted, to distinguishforward and backward movements, no additional means are needed fordetermining which key is pressed. Only the software that evaluates thedetector-signal undulations has to be adapted, which is a simple job forthe person skilled in the art.

The object or finger, which movement is to be measured is the scatteringor reflecting surface most remote from the laser cavity and is nowarranged at a considerably larger distance from the laser cavity. Thisprovides the great advantage that the number of zero-order undulationscaused by presence of the finger is considerably increased, whichlargely facilitates recognition of upward or downward scroll movement.In this way the quality and reliability of the scroll signal of theintegrated input device and optical keyboard is considerably increasedcompared with that of the input device per se.

As for the scroll/click signal the number of zero-order undulations islarger than the number of these undulations caused by any pressed key,the signal caused by a movement of the finger can easily bedistinguished from a signal caused by a pressed key.

FIG. 18 shows an embodiment 200 of the optical keyboard with integratedinput device, which comprises two diode lasers 202, 204 and associatedphoto diodes (not shown) . The input device can be used for measuring aclick movement and scroll movement either along one axis or along twoaxes. The keys 125 are now distributed over two groups. The condition ofthe keys of the first group, the lower group in FIG. 18, is now measuredby means of diode laser 202 and the associated detector. The measuringbeam 206 from this diode laser is guided along the positions of the keysof the first group by means of mirrors 210 and 212 and is then directedto the device window 186 by means of the mirrors 214 and 216. Diodelaser 204 and the associated detector are used to measure the conditionof the keys of the second group of keys, the upper group in FIG. 18. Themeasuring beam 208 is guided along the positions of these keys by meansof the mirrors 218 and 220 and is then directed to the device window bymeans of the mirrors 222 and 224. In this embodiment the position of apressed key is obtained by determining for which one of the measuringbeams the radiation path is interrupted and measuring the number ofzero-order undulations in the detector signal associated with thismeasuring beam.

FIG. 19 shows an embodiment 230 of the optical keyboard with anintegrated optical input device, which comprises three diode lasers 232,234, 236 and associated photo detectors (not shown) The keys 125 are nowdistributed over three parallel groups. The diode lasers are arrangedrelative to the groups such that the measuring beams 238, 239 and 240pass the positions of the keys of the first (left hand) group, thesecond (central) group and the third (right hand) group, respectively.Measuring beam 239 is directly incident on device window 186 andmeasuring beam 238 and measuring beam 240 is directed to this window bymeans of mirror 244 and mirror 246, respectively. As in the embodimentof FIG. 18, the position of a pressed key is obtained by determining forwhich one of the measuring beams the radiation path is interrupted andmeasuring the number of zero-order undulations in the detector signalassociated with this measuring beam. The measuring beams 238, 239 and240 can be used to measure scroll movement in the X direction, a scrollmovement in the Y direction and a click movement in the Z-direction,respectively. It is also possible to use one or two measuring beams tomeasure both a scroll movement and a click movement and to use the thirdmeasuring beam for obtaining additional information, for example toenhance the reliability with which one of the movements is measured.

Although the invention has been described at the hand of a mobile phoneapparatus, it can be used in several other apparatus, especially smallbattery powered apparatus comprising an optical input device and anoptical keyboard. An example of such an apparatus is a cordless phoneapparatus comprising the same or similar functions as the mobile phoneapparatus. A cordless phone apparatus 250 is shown in FIG. 20. Thisapparatus is composed of a base station 252, which is connected to aphone or cable network and the movable apparatus 254 which can be usedwithin an area with a radius of, for example, less than 100 m from thebase station. Apparatus 254 comprises an optical keyboard 256 and adisplay device 258. As is the case for the mobile phone apparatus, theapparatus 254 may be provided with the WAP protocol or the I-modeprotocol for access to the Internet and is provided with an opticalinput device 260. This input device, of which only the window is shown,is integrated with the optical keyboard as described herein above. Thedevice window may also be arranged in a side surface of the apparatus254. Like the mobile phone apparatus, the apparatus 254 should be smalland light-weight so that implementation of the invention in the cordlessphone apparatus provides the same advantages as in the mobile phoneapparatus.

The invention may also be used in a portable computer, known as notebookor laptop, an embodiment 270 of which is shown in FIG. 21. The notebookcomprises a base portion 272 and a cover portion 274 with a LCD display276. The base portion accommodates the different computer modules and anoptical keyboard 278. In this keyboard, an optical input device 280 isarranged which replaces the conventional mouse pad. The input device maybe arranged at the position of the conventional mouse pad or at anyother easily accessible position. The optical keyboard and the opticalinput device are integrated as described herein before for a mobilephone apparatus.

A hand-held computer, for example the type known as personal digitalassistant (DPA) is a smaller version of the notebook. Such a handheldcomputer may also be provided with an optical input device and otheroptical devices mentioned with respect to the notebook computer. As,moreover a hand-held computer should have smaller weight and size andconsume lesser energy than a notebook computer, use of the invention ina hand-held computer provides even larger advantages.

The invention can also be used in small-sized game computers.

FIG. 22 shows a desktop computer configuration 290 wherein an opticalinput device is used to replace the conventional trackball mouse. Theconfiguration is composed of a keyboard casing 292, a computer box 294and a monitor 296. The monitor may be a flat LCD monitor fixed in asupport 298, as shown in the Figure, or a CRT monitor. An optical inputdevice 302, of which only the device window is shown, is arranged in thekeyboard casing 292. According to the invention, the keyboard 300 is anoptical keyboard and the input device 302 is integrated with thekeyboard as described herein before.

The invention can also be used in a remote control unit 320 for use in aconventional TV set configuration 310, shown in FIG. 23 and whichcomprises a receiver and display apparatus 312 provided with a display314 and speakers 316. The configuration is equipped with a set top box318 to make the apparatus suitable for, for example, Internetcommunication. This box provides access to the Internet via a phone orcable network and converts the signal received from the Internet into asignal that can be processed by the TV set in order to display theInternet information. As a user of the Internet TV should have the inputdevice for Internet commands at hand, this input device 324 should beintegrated in the remote control unit 320. The number pad or keyboard322 of the remote control is an optical keyboard and, according to theinvention, the optical input device is integrated with the keyboard inthe way as described herein before.

In general, the invention can be used in any apparatus, which isequipped with an optical input device and an optical keyboard.

1. An apparatus comprising an optical input device controlled by amoving object near a window and an optical keyboard, wherein the opticalinput device comprises at least two optical sensor units comprising atleast two diode lasers for supplying at least two measuring beams andconverting means for converting measuring beam radiation reflected bythe object into an electric signal, which converting means areconstituted by the combination of a laser cavity and measuring means formeasuring changes in operation of the laser cavity, which are due tointerference of reflected measuring beam radiation re-entering the lasercavity and the optical wave in this cavity and which are representativeof the movement of the object, wherein at least two paths of the atleast two measuring beams from the at least two diode lasers to thewindow extend through at least two light guides of the optical keyboard,said at least two paths including mirrors and passing through thewindow, wherein each key of the optical keyboard along said at least twopaths is associated with only a single path of said at least two paths.2. The apparatus as claimed in claim 1, wherein the at least two sensorunits are arranged relative to the optical keyboard such that the atleast two measuring beams pass on their way to the device windowpositions of a first set of keys and positions of a second set of keys,respectively, the first set and the second set together comprising allkeys to be controlled.
 3. The apparatus as claimed in claim 1, whereinthe optical input device comprises at least three sensor units, whichare arranged relative to the optical keyboard such that at least threemeasuring beams of first, second and third sensor units pass, on theirway to the device window, positions of a first, a second and a third setof keys, respectively, the first, second and third set comprising allkeys to be controlled.
 4. The apparatus as claimed in claim 1, whereinthe at least one sensor unit of the two sensor units is adapted tomeasure both a scroll movement and a click movement and provided withadditional means, which allow establishing the presence of an object onthe window of the device.
 5. The apparatus as claimed in claim 4,wherein the additional means are constituted by means for establishingwhether the reflected measuring beam radiation shows an amplitudevariation of a frequency lower than the frequencies of variations causedby a scroll movement.
 6. The apparatus as claimed in claim 4, whereinthe additional means are constituted by electronic means for detecting acomponent in an output signal of said measuring means.
 7. The apparatusas claimed in claim 4, wherein said at least one sensor unit isactivated by activation pulses and the measuring means performmeasurements during time intervals determined by the activation pulses,wherein the additional means comprises counting means and comparingmeans to establish whether a number of undulations in the output signalmeasured during a first half and a second half of a said time intervalare equal.
 8. The apparatus as claimed in claim 5, wherein the said atleast one sensor unit comprises a first radiation-sensitive detector formeasuring variations in the laser cavity, wherein the additional meansis constituted by a second radiation-sensitive detector arranged forreceiving measuring beam radiation, which is non-incident on the lasercavity.
 9. The apparatus as claimed in claim 5, wherein aradiation-sensitive detector is arranged at a rear side of the lasercavity.
 10. The apparatus as claimed in claim 8, wherein the seconddetector is arranged at a side of the laser cavity where the measuringbeam is emitted.
 11. The apparatus as claimed in claim 1, wherein themeasuring means of the optical input device are means for measuring avariation of an impedance of the laser cavity.
 12. The apparatus asclaimed in claim 1, wherein the measuring means is a radiation-sensitivedetector for measuring radiaation emitted by one laser diode of the atleast two diode lasers.
 13. The apparatus as claimed in claim 1, whereinthe apparatus is a mobile phone.
 14. The apparatus as claimed in claim1, wherein the apparatus is a cordless phone.
 15. The apparatus asclaimed in claim 1, wherein the apparatus is a laptop computer.
 16. Theapparatus as claimed in claim 1, wherein the apparatus is a hand-heldcomputer.
 17. The apparatus as claimed in claim 1, wherein the apparatusis a keyboard for a desk computer.
 18. The apparatus as claimed in claim1, wherein the apparatus is a remote control for a TV set.
 19. Theapparatus of claim 1, wherein one of the at least two light guidesincludes a protruding element, such that one of the at least twomeasuring beams is coupled into the optical keyboard only at positionswhere the at least two paths cross each other, the positions includingrecessions.
 20. The apparatus of claim 1, wherein the least two opticalsensor units are configured to measure changes in the at least twomeasuring beams for determining which key of the optical keyboard ispushed.
 21. An apparatus having an optical keyboard and an optical inputdevice controlled by a moving object near a window, the optical inputdevice comprising at least two optical sensor units including at leasttwo diode lasers for supplying at least two measuring beams andconverting means for converting a reflected beam reflected by the movingobject into an electric signal, wherein at least two paths of themeasuring beam from the at least two diode lasers to the window includemirrors and pass through the window, wherein each key of the opticalkeyboard along said at least two paths is associated with only a singlepath of said at least two paths.
 22. The apparatus of claim 21, whereinthe at least two paths are independent from each other and meet only atthe window.
 23. An optical input device controllable by a moving objectnear a window of an optical keyboard, the optical input devicecomprising: at least two diode lasers for supplying a measuring beam forreflection from the moving object; and at least two detectors configuredto convert a reflected beam reflected by the moving object into anelectric signal, wherein at least two paths of the measuring beam fromthe at least two diode lasers to the window include mirrors and passthrough the window wherein each key of the optical keyboard along saidat least two paths is associated with only a single path of said atleast two paths.
 24. The apparatus of claim 1, wherein the at least twoguides are independent from each other and meet only at the window. 25.The optical input device of claim 23, wherein the at least two paths areindependent from each other and meet only at the window.